Using the CLEO detector at the Cornell Electron Storage Ring, the authors have measured the leptonic branching fractions, $B_{\mu \mu }$, of the $\Upsilon \mathrm{}\left(1S\right)\mathrm{}$, $\Upsilon \mathrm{}\left(2S\right)\mathrm{}$, and $\Upsilon \mathrm{}\left(3S\right)\mathrm{}$ to be 2.7±0.3±0.3%, 1.9±1.3±0.5%, and 3.3±1.3±0.7%, respectively. Combining these values of $B_{\mu \mu }$ with previous measurements of the leptonic widths of these resonances, the authors find the total widths of the $\Upsilon \mathrm{}\left(1S\right)\mathrm{}$, $\Upsilon \mathrm{}\left(2S\right)\mathrm{}$, and $\Upsilon \mathrm{}\left(3S\right)\mathrm{}$ to be 48±4±4, 27±17±6, and 13±4±3 keV.

• Received 6 January 1983

DOI:https://doi.org/10.1103/PhysRevLett.50.807